To investigate the effect of chitosan oligosaccharide on melanin synthesis, we measured tyrosinase activity and melanin production in B16 melanoma cells. Chitosan oligosacchaide itself did not have any anti-oxidant activity in DPPH radical scavenging, and did not affect the proliferation of B16 melanoma cells. Chitosan oligosaccharide dose-dependently increased melanin production in the absence or presence of MSH. However, chitosan oligosaccharide did not have any influence on the tyrosinase activity and tyrosinase expression in B16 melanoma cells. These results suggest that chitosan oligosaccharide-induced melanin production may be independent on tyrosinase activity in B16 melanoma cells. From the above results. chitosan oligosaccharide dose-dependently appears to increase melanin production in B16 melanoma cells, suggesting that chitosan oligosaccharide may be used as a tanning agent.